AT&T and Time Warner announced their merger agreement last year, but the closing has been dragged out by the government's antitrust review.

A Justice Department official told reporters on Monday that the merger would raise prices for consumers and potentially block creators of media content from distributing their product without paying more money. Time Warner owns various networks in addition to CNN, including TBS, TNT and Cartoon Network. It also has lucrative sports broadcasting deals.

—CNBC's Liz Moyer contributed to this report.

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